From: Henry Spencer <henry@zoo.toronto.edu>
Newsgroups: sci.space.tech
Subject: Re: Hypergolic pressurisation
Date: Mon, 15 Jul 1996 15:36:21 GMT

In article <4s4h1g$b1a@infoserv.rug.ac.be> FilipPC.DeVos@rug.ac.be (Filip De Vos) writes:
>The main advantage I see in using a controlled fire in side a propellant 
>tank to pressurise it, is to reduce the amount of gas needed. 

The idea is not new, actually.  Unfortunately, it's difficult to make it
work well, which is why it's not more widely used.

The real trick is temperature control.  What reduces the amount of gas is
keeping the gas hot, not generating it within the tank.  Moreover, the gas
from hypergolic reactions tends to contain easily-condensible things like
water, so you *must* keep the gas hot if this is all to work.  However, you
have to keep the temperature down below levels that endanger the tank walls.
*And* you have to do this in the presence of a large, and possibly turbulent,
surface of cool liquid.

This is a little tricky even if you're using a separate gas generator,
so that the gas-generation reaction at least occurs under controlled
conditions.  Injection into the main tank complicates the situation
greatly, making adequate control very doubtful. 

Many pressurization systems heat the gas, but usually it's a whole lot
easier to use an inert and non-condensible gas -- that way, inadequate
temperature control is just a gas-wasting nuisance, not a disaster.
-- 
..the truly fundamental discoveries seldom        |       Henry Spencer
occur where we have decided to look.  --B. Forman  |   henry@zoo.toronto.edu